Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Remote Access Data Communications/Networking ©Richard L. Goldman February 13, 2002 Page 1 - © Richard L. Goldman Remote Access • Remote access technologies allow users to access a network and its services from a computer outside the network • Dial-up access requires: – Network computer (server) running RAS or NAS with a modem and a dial-up phone line • Remote Access Server – Microsoft • Network Access Server – Novell – Remote computer (laptop) with modem and a dial-up phone line – An ISP is not required – This will be a direct “call” from one computer to another computer. Page 2 - © Richard L. Goldman Types of Modulation • AM – Amplitude Modulation • FM – Frequency Modulation • PM – Phase Modulation – PSK – Phase Shift Keying – Shifts with bit change – DPSK – Differential Phase Shift Keying – Shifts when a “1” bit is to be transmitted. • PCM – Pulse Code Modulation – Method used by CODEC – Digital “1” is twice the voltage of a digital “0”. Page 3 - © Richard L. Goldman Types of Multiplexing • FDM – Frequency Division Multiplexing • WDM – Wave Division Multiplexing • TDM – Time Division Multiplexing • STDM – Statistical Time Division Multiplexing Page 4 - © Richard L. Goldman Modems • Modulator-demodulator • Converts digital to analog for transmission over POTS (Plain old Telephone Service) • Configure: – COM 1 or 3 – IRQ 4 – I/O 3F8 or 3E8 – COM 2 or 4 – IRQ 3 – I/O 2F8 or 2E8 • Internal Modems – Have built in UART (Universal Asynchronous Receiver-Transmitter) – Usually new (16550 or newer) – Cheaper • External Modems – – – – Uses computer's internal UART – may be old (8250 - 9600bps max) and slow May be easier to configure Stats lights More expensive (case, power supply, cables, etc.) Page 5 - © Richard L. Goldman ISDN – Integrated Services Digital Network • • • • • Can carry voice and data simultaneously Uses a standard PSTN voice line Standard established by the ITU ISDN service began in mid 1980’s Requires a Network Termination device(s) to process the data from the telephone company • Requires a Terminal Adapter (router) to convert the digital data to voice and distribute the communication. • Must be within 3.4 miles (18,000 feet or 5.5Km) of the telephone company. Page 6 - © Richard L. Goldman BRI (Basic Rate ISDN) • Basic Rate (2B+D) ISND lines uses two B channels and one D channel multiplexed over 1 copper pair • Each B (Bearer) channels can transmit up to 64Kbps of data or it can be used to transmit voice. • The D (Data) channel can transmit up 16Kbps and is used for call setup & management • Two B channels can be bonded to produce 128Kbps throughput. NT1 Data TelCo 2 B channels 1 D channel Router Voice Page 7 - © Richard L. Goldman PRI (Primary Rate ISDN) • Primary Rate (23B+D) ISND lines uses 23 B channels and one D channel multiplexed over 1 copper pair • Each B (Bearer) channels can transmit up to 64Kbps of data or it can be used to transmit voice. • The D (Data) channel can transmit up 16Kbps and is used for call setup & management • The B channels can be bonded to produce 1.544Mbps throughput. NT1 NT2 TelCo 23 B channels 1 D channel Data Router Voice Page 8 - © Richard L. Goldman DSL – Digital Subscriber Line • Uses regular POTS “phone” lines to transmit digital signals • Allows voice and digital over single pair – Uses 0-4KHz for voice – Uses 4KHz-2.2MHz for data • ADSL – Asymmetric DSL – 640Kbps Uplink speed – 1.544Mbps Downlink speed (9Mbps Max.) • HDSL – High Data-Rate DSL • VDSL – Very High Data-Rate DSL • SDSL – Single Line Digital Subscriber Line Page 9 - © Richard L. Goldman Remote Access Protocols • SLIP – Serial Line Internet Protocol – – – – Used to transmit TCP/IP over serial connections Low overhead – No error checking – No packet addressing Being replaced with more feature rich protocols Does not support encrypted passwords • PPP – Point-to-Point Protocol – Used to implement TCP/IP over point-to-point connections – uses the Link Control Protocol (LCP) to communicate between PPP client and host – high overhead – automatically configures TCP/IP • PPTP – Point-to-Point Tunneling Protocol – PPTP is setup through a PPP connection forming a VPN Page 10 - © Richard L. Goldman PSTS “Demarc” (Demarcation Point) Local Loop (UTP) Central Office Local Switch POP Regional Switch Long Distance Switch POP Page 11 - © Richard L. Goldman X.25 Protocol • Analog WAN technology employing packet switching • Sending router breaks messages into smaller packets • Packets may travel different routes • Developed CCIT (now ITU) • Handles bottom 3 layers only Page 12 - © Richard L. Goldman Frame Relay • Digital WAN technology employing packet switching • Sending router breaks messages into smaller packets • Packets may travel different routes • Receiving router reassembles packets • By sharing the network you get the minimum that you contract for (Committed Information Rate CIR) but may receive speeds up to T1 speed Page 13 - © Richard L. Goldman T-Series Connections • T-1 - 1.544Mbps – 2 pair STP(or UTP) – 24 DSO channels - (64Kbps each) • T-1C - 3.152Mbps • T-2 - 6.312Mbps • T-3 - 44.736Mbps - Fiber or Microwave – 672 DSO channels • T-4 - 274.176Mbps Page 14 - © Richard L. Goldman Remote Connection Terms • • • • • • • • • • • • • • • Asymmetrical Asynchronous CODEC CSU/DSU Demarc DSL ISDN Modem Mux POP POTS PSTN RAS UART VPN Not Symmetrical Not Synchronous Coder/Decoder Channel Service Unit/Data Service Unit Demarcation Point Digital Subscriber Line Integrated Services Digital Network Modulator/Demodulator Multiplexer Point of Presence Plane Old Telephone Services Public Switched Telephone Network Remote Access Service Universal Asynchronous Receiver-Transmitter Virtual Private Network Page 15 - © Richard L. Goldman